What Is Selective Focus?
A basic technique, it is essentially the photographer selecting a particular object or subject to put focus on. Not only do you focus on that particular object but you ignore every other aspect in the scene as well.
With a shallow depth of field, the selection is then in a sharper focus while the rest of the scene is blurred out of focus. The idea is to draw the attention of the view to that specific object or subject. For scenes that may feel busy, unattractive, or distracting, it can be a powerful way to put focus on a specific person or object.
For even more powerful images, you can try to contrast an object sharply in front of a background that has been blurred out. The key is finding the balance so as to make the blurry background complementary to the focused image.
How Do You Use Selective Focus?
While it may seem as though the sharper aspect of the image is the important part, the out-of-focus area is just as important to the image. Without those out-of-focus areas, there is no selective or differential focus.
Thankfully, camera manufacturers have put a lot of time, money, and research into the development of lenses that can selectively focus. Some older cameras, ones without automatic selective focus, could be manipulated but it takes skill and patience to execute.
Now, there are a ton of different ways to change, use, and create that selective focus within your images. Long lenses, open apertures, and changing the depth of field are some of the most consistent ways to do so. You can also keep the subject separate from the background, change the angle, or move closer to the subject.
Depth of Field
Images that have a selective focus tend to have a shallow depth of field. This means that the camera’s range of focus is quite small. So, if the subject was 10 feet from your camera with the camera set at f/1.2, then you can expect to see a near limit of 9.74 ft with a far limit of 10.3. Everything in that 0.54 ft between will be in sharp focus.
Determining depth of field is an interchangeable setting within most modern cameras. Range of focus can also change as it depends on the subject’s distance from the camera. Depending on where the subject moves, the amount of focus can rise or shrink.
There are also wide-open apertures that place a smaller focal range on a given scene. This means that less of the scene, object, or subject gets put into focus. The aforementioned f/1.2 has the capability of capturing the eyes of a person in focus while keeping the ears and nose out of focus.
Narrower apertures put more of the scene into greater focus. Going above f/16 puts everything in the scene into focus, but there are some issues that are worth considering in that event.
One issue is that there are lenses out there with sharper F-stops than some other types of camera. And with zoom lenses, it is possible that some apertures are not quite as sharp as others. The other issue is that the faster lenses out there tend to deal with chromatic aberrations, which is when there are red/purple/blue/green/cyan fringes in the shot.
Another option for getting selective focusing is a longer lens. Longer lenses can also impact your ability to capture those scenes in selective focus. Lower-end telephoto lenses do come with variable apertures, however.
Basically, the longer zoom means that there is a smaller field of view. When there is a smaller field of view, the aperture is narrower. When a wider aperture is required, that can mean a lesser amount of focus than is otherwise desired.
There is also the consideration that any lens can potentially soften the background in a given scene, so long as the background and the distance between you and the subject allows for such considerations.
The closer the camera is to the subject, the blurrier everything gets. Similarly, the same thing happens when there is more distance between the subject and their background. That is why lens choice is of the utmost importance.